Coupling devices for coupling accessories to hydraulically operated arms of excavator machinery are well known. These devices are typically used to attach different types of attachments to a mechanical arm (commonly referred to as the “dipper arm”) of such apparatus. Such attachments may include, but are not limited to, a rock breaker, or different sizes of buckets.
The coupling device (also commonly referred to as a “coupler” or “quick hitch”) is usually releasably attachable to both the (dipper) arm of an excavator and the attachment. The quick hitch is adapted for attachment to the arm and normally would remain on the arm and be utilised to interchangeably couple different attachments to the arm. Typically, quick hitches come in one of two configurations: “pin couplers”, and “dedicated couplers”.
Dedicated couplers are usually configured to interact only with attachments bearing complementary components, these complementary components often comprising combinations of plates and holes. Pin couplers, on the other hand, are designed to work in conjunction with any attachment bearing a pair of spaced apart coupling pins typically used for connecting to arms. Pin couplers comprise a body member adapted for coupling to the arm, and a pair of engagement members that are provided for releasably engaging the pair of spaced apart coupling pins located on the attachment. One engagement member typically is moveable relative to the other engagement member between an engaged state and a disengaged state. In the engaged state, the engagement members co-operate such that each engagement member securely engages a respective coupling pin, thereby securely coupling the attachment to the dipper arm. In the disengaged state, the engagement members are positioned relative to one another such that the coupling pins are not securely engaged, and the attachment can thereby be released from the dipper arm. The engagement members are formed, for example, by a set of hooks, typically at least two hooks. Typically, the moveable engagement member is either slideably or pivotally connected to the body member and is moveable between the engaged and disengaged states by a ram, for example, a hydraulic means such as a hydraulic ram, or by mechanical means, such as a ram comprising a screw threaded piston, a linkage or a lever. Pin couplers comprising hydraulic means, and dedicated couplers analogously comprising hydraulic means will herein be referred to as “hydraulic couplers”, whereas pin couplers comprising mechanical means, and dedicated couplers analogously comprising mechanical means will herein be referred to as “mechanical couplers”.
Pin couplers and dedicated couplers suffer from a number of disadvantages.
To avoid the inadvertent or accidental release of the attachment by releasing the grip of the coupler on the attachment, locking systems have been incorporated into existing coupling systems to ensure that the attachment is only released when it is desired to do so. Mechanical locks have been provided on couplers that require the operator of the machine (or another person) to manually release the mechanical lock. Such mechanical locks have been provided in both mechanical and hydraulic couplers. However, the operator must get out of the excavator machine to operate the lock, and this is not always done. A problem therefore arises when the operator of the excavator neglects to engage the lock after connecting an attachment to an excavator arm.
Irish Patent Number 2005/0169 discloses a quick attachment device in which a safety lock may be engaged and disengaged by an operator, however manual intervention on behalf of a user is required to engage and disengage the lock. Furthermore, the lock may close even when there is no attachment secured in place. It would be preferable to provide an attachment device which overcomes the drawbacks outlined above.